Heat resisting nickel-aluminum-molybdenum alloy

ABSTRACT

A nickel base heat resisting alloy having high tensile strength and excellent oxidation resistance at high temperatures in the range of 1,000*-1,200*C and toughness at room temperature characterized by the alloy comprising 91-99.9 atomic percent of a basic constituent, up to 6 atomic percent silicon, and between 0.1-3 atomic percent of a second or additive constituent consisting of one or more elements selected from a group of elements consisting of titanium, chromium, zirconium, niobium, tantalum and tungsten. The basic constituent comprises nickel, aluminum and molybdenum in the following atomic percents of the basic constituent: nickel 62-83%, aluminum 11-26%, and molybdenum 6-12%. In one embodiment, the silicon comprises 0% and the basic constituent comprises between 97-99.9 atomic percent of the alloy. In the other embodiment, the silicon is in a range of 0.56 atomic percent and the basic constituent is in a range of 9199.4 atomic percent of the alloy. The addition of the silicon improves the oxidation resistance of the alloy when heated to an elevated temperature.

United States Patent [191 Komatsu et al.

1 1 HEAT RESISTING NICKEL-ALUMINUM-MOLYBDENUM ALLOY 175] Inventors: Noboru Komatsu; Takatoshi Suzuki;

Nobuyuki Yamamoto; Yukikazu Tsuzuki, all of Nagoya, Japan [73] Assignee: Kahushiki Kaisha Toyota Chuo Kenkyusho, Japan [22] Filed: Dec. 5, 1973 [21] App]. No: 421,971

Primal; litumirwr-R. Dean Attorney, Agent or Firm--Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson 1 51 Sept. 9, 1975 ABSTRACT A nickel base heat resisting alloy having high tensile strength and excellent oxidation resistance at high temperatures in the range of l ()0U*l 200C and toughness at room temperature characterized by the alloy comprising 91-999 atomic percent of a basic constituent, up to 6 atomic percent silicon, and between 0.1-3 atomic percent of a second or additive constituent consisting of one or more elements se lected from a group of elements consisting of titanium, chromium, zirconium, niobium tantalum and tungsten. The basic constituent comprises nickel alumi num and molybdenum in the following atomic pcrcents of the basic constituent: nickel 62-83% alumi num 11-26% and molybdenum 6-1271. In one cmbotliment, the silicon comprises ()'7( and the basic constituent comprises between 97-999 atomic percent of the alloy. 1n the other embodiment, the silicon is in a range of (J.56 atomic percent and the basic constituent is in a range of 91-994 atomic percent of the alloy. The addition of the silicon improves the oxidation resistance of the alloy when heated to an elevated temperature 15 Claims, 8 Drawing Figures PATENTED SEP 91975 3. 9 O4. 40 3 Alur/.%

PATENTED 9i975 3.904.403

sum 3 0r 4 fensi/e .s frengzh (K /mm O l l I l I J l Mo confenf fe nsf/e sfr'eng 1% (kg/mm r In T 1 1 l O 1 2 3 4 5 can fen fofac/difi'ue e/emenf) IIEQ. I RESISTI Nb N lCKEL-ALU MINU l\ I-NIO] .Y BDENUM ALLOY BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to a heat resistant nickel base alloy having a high tensile strength at high temperatures and toughness at room temperature.

" Prior Art A number of equipments and parts to be employed at high temperatures exceeding 1.000% has increased as the result ofthe industrial progress and technical advancements attained during recent years. There are ever-increasing demands for heat resisting materials that can be used for parts exposed to high temperatures and heavy loads. Examples of devices which require heat resisting materials are rocket shells. atomic energy engines. combustion chambers and jet tubes or pipes for jet engines. parts of gas turbines. high temperature and high pressure apparatuses used in the chemical industries and high temperature valves. To meet the requirements for heat resisting materials. many technical studies ha\e been conducted and. thus. many kind of heat resisting materials have been suggested. It is generally belicv ed that heat resisting steels are applicable for use tor a temperature below 800C and that heat resisting alloys containing either nickel (Ni) or cobalt (Co) as the principle component may be used up to a temperature of l.00()(. When used at temperatures higher than the above-mentioned temperatures, these alloys experience a deterioration in strength and therefore. their use is limited to a temperature range which does not exceed the above-mentioned temperature In addition. the manufacture of most of these conventional alloys can involve many difficulties. for example. many of these alloys must be melted in a vacuum.

Heat resisting metal alloys. such as molybdenum (Mo). niobium (Nb) and tantalum (Ta) or ceramics may serve for a long period of time at elevated temperatures above [000 C The metal alloys are inferior in their resistance to oxidation at elevated temperatures and thus are limited in their use to atmosphere or service conditions in which oxidation is not present. If they are to be used in oxidizing atmosphere, the alloy must be provided with a surface treatment for the prevention of oxidation. The ceramics have a disadvantage of a lack ofductility and thermal impact resistance. For example. ceramics will tend to break due to a sudden change in temperature. Thus. the actual use of conventional refractory or heat resisting materials at elevated temperatures posses many shortcomings and many problems with oxidation and strength at elevated temperatures still existv SUMMARY OF THE INVENTION The present invention is directed to providing a heat resisting alloy or alloys which are free from the drawbacks of the conventional heat resisting alloys as described hereinabovc and which alloys have excellent mechanical strength. toughness and oxidation resistance at elevated temperatures ranging from i.i)00-l.200C. Alloys of the present invention comprise )l-Ql) atomic percent of a basic constituent, 0. l 3 atomic percent of an additive or second constituent and up to atomic percent silicon. The basic con stituent comprises nickel. aluminum and molybdenum in the following atomic peicents of the basic eonstittr ent: nickel 6283"/(. aluminum 1 1-26'79 and molybdenum 642%. The additive or second constituent con sists of at least one element selected from a group of el ements consisting of titanium, chromium. zirconium. niobium, tantalum and tungsten. If oxidation resistance is not a problem. the addition of the silicon can be eliminated so that the alloy contains 0 atomic percent silicon and the basic constituent will then have an atomic percent of 97-999 atomic percent of the alloy. When the silicon is required. between 0.56 atomic percent is added and the basic constituent then comprises 91-994 atomic percent of the alloy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a triangular coordinate diagram which rep resents by atomic percent the range of composition of the nickel. aluminum and molybdenum of the basic component or constituent of the nickel base alloy of the present invention;

FIG. 2 is a triangular coordinate diagram representing in weight percent the range of composition of the nickel. aluminum and molybdenum of the basic com ponent or constituent of the nickel base alloy of the present invention;

FIG. 3 is a cross-sectional view oi'a metal melting de vice utilized in preparing a Lini-direetionally solidified rod to be used in tensile tests and other tests performed on the alloys of the present invention;

FIG. 4 is a graph illustrating the change in tensile strength at l.()()0C of different nickel-aluminum molybdenum alloys in relationship to a variation of the content of molybdenum;

FIG. 5 is a graph illustrating the effect of changes in the molybdenum contact in a niekel-aluminummolybdenum alloy on the measuring loads used in a toughness test at room temperature; I

FIG. 6 is ,a graph illustrating the effect of adding dif fcrent amounts of one or more additive elements of titanium. chromium. Zirconium. niobium. tantalum and tungsten to a nickel-aluminum-molybdenum alloy on the tensile strength at l.l()()C-.

FIG. 7 is a graph illustrating the effect of different amounts of silicon in a nickcl-aluminum-molybdcnum alloy of the present invention on the weight increase due to oxidation when the alloy is subjected to heating at [200C for 21 hours;

FIG. 8 is a graph illustrating the changes in tensile strength at I,IOUC of the alloy of the present invention containing silicon with respect to changes in the content of silicon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the present invention are particularly useful for providing nickel base heat resisting al Ioys having a main or base constituent or component comprising nickel. aluminum and molybdenum with a second constituent or additive consisting of one or more elements selected from a group of elements consisting of titanium, chromium. Zirconium. niobium. tantalum or tungsten with or without the addition of silicon which improves the resistance of the alloy to oxidation. The alloys of the present invention are a result of a study which was concentrated on improving the prop ertics of conventional heat resisting alloys and particularly an improving of the alloys high temperature ten- 3 r sile strength characteristics and their toughness at room temperature. The study utilized the knowledge that an intermetallic compound of nickel and aluminum alloy, which has the formula of Ni;,Al. has an excellent resistance to oxidation at elevated temperatures when compared with conventional heat resisting alloys. The additive elements of the alloy of the present invention are for the purpose of increasing the high temperature tensile strength of the Ni;.Al alloy and the tough ness at room temperatures. In addition to the additives of the second constituent. an embodiment of the alloys of the present invention includes the addition of a small quantity of silicon to increase the resistance to oxidation without detrimcntally affecting the high temperature tensile strength properties.

A nickel base alloy having the following composition presents high tensile strengths at elevated temperatures as well as excellent toughness at room temperatures. The composition consists principally of nickel. aluminum and molybdenum having atomic percent of the basic component or constituent of the alloy with the percentages being enclosed by the straight lines con necting points A. B. C and D in an equilateral triangular coordinate diagram illustrated in FIG. I. The point A in FIG. 1 represents an alloy having 83% nickel. l 19 aluminum and 6% molybdenum; point B represents an alloy having 68% nickel. 26% aluminum and 6% molybdenum; point C represents an alloy having 62% nickel. 26% aluminum and 12% molybdenum; and point D repr'esents an alloy having 77% nickel. ll'/( aluminum and 12% molybdenum. In addition to the basic component or constituent the alloy of the present invention includes at least an additive or second con -stituent which consists of at least one element selected from a group of elements consisting of titanium. chro mium. zirconium. niobium. tantalum and tungsten with the basic component or constituent ranging from 97-999 atomicpcrccnt and the contents of the additive or second constituent ranging from 0. l-3 atomic percent. In addition. it has been found that an embodiment of the alloys of the present invention containing 9 [-99.4 atomic percent of the basic component or constituent. from 0. l-3 atomic percent of the additive constituent and from 0.56 atomic percent of silicon pres- 'ents an appreciable high resistance to oxidation at elevated temperatures in addition to the high tensile strength at elevated temperatures and high toughness at roorn temperatures.

The triangular coordinate diagram of FIG. I is an equilateral triangular coordinate diagram with three sides having equal divided gradations to show the relationship between the content of nickel. aluminum and molybdenum for alloys containing more than atomic percent of nickel. In the diagram of FIG. 1, the atomic percent of aluminum is plotted on the base of the UL angular coordinate diagram. the atomic percent of the nickel is on the left side. and the atomic percent of the i molybdenum is on the right side. Accordingly, the content of aluminum (percentages) is represented by a line extending parallel to the left side. the content of the nickel is r'cpresented by a line extending parallel to the right side and the content of molybdenum is represented by a line extending parallel to the base. For example. a point Y in FIG. 1 represents a composition consisting of 709? nickel. 10)? aluminum and molybdenum. i

The proportions of the respective elements illustrated in FIG. 1 represent the ratio of the elements in the basic constituent; but not the ratio of the elements in an alloy which includes the additive elements. For example. if an alloy contains 98% of the basic constituent. an additive constituent of 2V: titanium and the basic constituent consists of nickel. 10% aluminum and 10% molybdenum. the atomic percentage of the elements of the basic constituent in the alloy are: nickel 70 X 0.98 68.6 atomic percent. aluminum 20 X (1.98 19.6 percent. molybdenum It) X 0.98 9.8 percent. and titanium is 2%.

Hercinabove. the amount of nickel. aluminum and molybdenum in the alloys of the present invention have been expressed in atomic percent of the basic constituent which may between 9 [-99.9 atomic percent of the alloy. Using the above described calculation. the alloys of the present invention can be described in atomic percent range of the alloy as follows: nickel 56.42-82.9l7r; aluminum lU.0I25.974'/r; molybdenum S.46ll.988'/(; additive constituent (1.l3"r; and silicon (l-fi'7r. If silicon is not present. the alloys of the present invention will have the following range of atomic percents for the elements of the basic constituent: nickel 6U.l482.9l'/r alumin'uni ll).o7-2S.974l; and molybdenum 5.824 1.988%. If silicon is present. the alloys of the present invention will have the follow ing ranges of atomic percents for the element of the basic constituent: nickel Sb.42-82.5ll2'/r; aluminum MIDI-25.84471; and molybdenum 5.46% IFJZSQ. It should be noted that if the additive constituent is (I. l i and silicon is not present or only 0.5%. the difference between the total percentage of the elements of the base constituents in the alloy and their percentage in the base constituent is extremely small.

For reference purposes. an equilateral triangular coordinate diagram which represents the ratio of nickel. aluminum. molybdenum by weight percent is shown in FIG. 2. The points A. B, C and D in FIG. Zrepresent the same compositions as those in points A. B. C and D of FIG. 1.

The quantity of aluminum in the basic constituent of a nickel base alloy according to the present invention is restricted to a range of between Hand 26% for the following reasons. It is well known that a nickel base heat resisting alloy. which consists of only -y phase at a desired high temperature, will include a solid solution of the other elements in the nickel and the alloy cannot achieve the desired strength. To achieve the increased tensile strength for the alloy at high temperature. at least a precipirate such as Ni Al must be dispersed in the phase or the Ni Al should be the principal component of the alloy. The presence of such a precipitate in a solid solution of nickel is an important factor to obtain the improved tensile strength at high temperature. Nickclaluminum-molybdenum alloys having a compo sition with a range represented on the left hand side of the curve 6 (FIG. 1 are alloy compositions which have a low content of aluminum and are of alloy composi tions in which only the y phase is present at room temperature. At l.20()C. the 'y phase is present in all alloys which are in the area of the diagram of FIG. I on the left hand side of the curvcfand at the I.ZO()C. the tensile strength of the nickel-aluminum-molybdcnum alloys having the composition within the range represented on the left hand side of the curve f is very low. In view of this information set forth above. the basic constituent of the alloy of the present invention which constituent consists of nickel-alummum-molybdenum has aluminum in an atomic percentage of more than l 1' 1 so that the 1 phase and the Ni;;Al coexist at l.2()l)C. In the area of the right hand side of a curve g (FIG. 1) and particularly the area where the content of the molybdenum is low. the alloys contain only a solid solution of NiAl in w hich nickel and molybdenum are dissolved (this solution is hereafter referred to as y phase). The nickel-alummum-molybdenum alloy having the composition within this range has extremely low tensile strength at elevated temperaturesv Likewise in the area of the diagram of FIG. 1 on the right hand side of the curve g in which area the content of molybdenum is high. the alloy when at about l.2(10C contains eutectic crystals of the y phase and the molybdenum with nickel and aluminum solidly dissolved therein and thus the alloy becomes very brittle and weak as the temperature increases. Specifically, when the phase is suddenly cooled from the elevated temperatures. there takes place a Martcnsite type transformation and the alloy composed of the 7' phase is hardened and bc comes extremely brittle. For example, the basic alloy of nickelaluminum-molybdcnum alloys of this invention contain less than 26% aluminum and provided toughness of more than 50 kg according to a toughness test method which will be described hereinafter. While a nickel-aluminum-molybdcnum alloy having a composition at a point P of FIG. 1 (50% nickel, 45% aluminum. 5% molybdenum) has a low toughness of about 1 to lt) kg. Accordingly. in the basic constituent of nickelaluminum-molybdenum of the alloy of this invention. the quantity of aluminum. is limited to less than 26% which is within the area of the left side of the curve g.

The quantity of molybdenum in the basic constituent is limited to a range of from 6-l2 atomic percent as shown in FIG 1. This is hecause nickcl-aluminummolybdenum alloy containing from 61-12% molybdenum have particularly high tensile strength at high temperatures and display an excellent toughness at room temperatures. When the amount of molybdenum in the basic constituent is increased and the constituent contains mainly Ni;,Al. the resulting nickcl-aluminummolybdenum alloys present peak values and high temperature tensile strength for a molybdenum content in a range of from 6l27(. Thus the quantity of molybdenum is limited to the range of 6-12 atomic percent.

In view of the reasons set forth hereinabove. the composition of the basic nickel-alurninum-molybdenurn which is the basic constituent or component of the nickel base heat resisting alloy ofthis invention are limited to a range of from 68-83% nickel. l [-26% aluminum and 6-12'7r molybdenum.

The nickel base alloy of the present invention contains a second or additive constituent or component in an amount of 0. l3 atomic percent which constituent Consists of one or more elements selected from a group of elements consisting of titanium. chromium. zirconium. noibium, tantalum. tungsten. The addition of the second component or constituent provides extremely high tensile strengths at elevated temperatures. It is believed that the increase in the high tensile strength at high temperatures is based on the fact that the nickelaluminum-molybdenum alloy is reinforced by dissolving one or more of the additive elements into the alloy as a solid solution. Namely atoms of one or more ofthc additive elements dissolve in the alloy are consid- (ill ered to be present as a solid solution in place of atoms of the elements forming the nickel-aluminum molybdenum alloy and thereby strengthen the alloy structure. The desirable affect appears when the quantity of the additive constituent is from 0.l3 atomic percent. The addition of less than 0.1% of the additive constituent exerts little influence on the strength of the alloy. The addition of more than 3% causes the formation of globulars or a square-flake shape crystalline structure of a large grain size in the dense structure of the nickel-a]uminum-molybdenum alloy. It is considered that when a stress acts on the alloys having the large crystalline structure. the stresses will be concentrated on the large crystalline structure of the alloys and cause breakage of the alloy to occur. This is obvious from the fact that the addition of the additive elements in excess of 3% causes an abrupt decrease in the high temperature strength of the alloy. According to the results of a hardness test, it is perceived that with an increase in the quantity of the additive element or elements. the hardness gradually increases. but when the addition is more than 3%. the hardness abruptly dccrcases or the increase of the hardness tends to stop. The effect of the additive constituent occurs whether the additive elements of the group is added individually or in a mixture of one or more elements from the group. However. when more than one of the elements is added to the alloy. the total content of the elements should not exceed 3 atomic percent since the addition of more than 3% leads to the unfavorable phenomena described hereinabove.

In addition to the above-mentioned additive elements of the additive constituents. tests were conducted using boron as an additive element for the basic Ni-Al-Mo alloy. However, the boron did not appear to affect the high temperature tensile strength of the alloy. Therefore. the alloys of the present invention may contain a small amount of boron as an impurity.

An embodiment of the alloys of the present invention contain the basic component or constituent of nickelaluminum-molybdcnum. (ll-3% of the additive constituent or component and from (XS-6% of silicon and these alloys not only display high strength at elevated temperatures. toughness at room temperatures. but also have excellent oxidation resistance at elevated temperatures. The addition of the silicon greatly improves the oxidation rcsistance of the nickel base alloy of the present invention. The addition of between (LS-6% silicon is greatly effective and the addition of from 2-47( silicon will provide the maximum oxidation resistance for the alloy. The addition of silicon less than i 0.5% or more than 6% is improper for use in improving oxidation resistance. The addition of the silicon to the alloy causes a slight decrease in the strength of the alloy at elevated temperatures. However. the effect and the improvement in the oxidation resistance is far greater despite the decrease in strength at high temperatures.

The heat resisting alloys of the present invention will be further explained with the following test examples and embodiments showing the mechanical strength of the inventive alloy. Each of the alloys for the test samples of the following examples and embodiments was obtained from raw materials consisting of electrolytic nickel. high purity aluminum. high purity molybdenum. and high purity raw materials of the additi\e elements such as titanium. chromium. zirconium. niobium. tantalum and tungsten. These raw materials were subjectcd to a high frequency melting in an alumina cruci ble under a protective atmosphere of argon gas and the resultant molten metal was cast into a cast product. The cast product thus attained was subjected to oxidation resistance tests. tensile tests and hardness tests which will each be described hereinbelow.

It is known that the mechanical properties of Ni;.AI greatly vary with the solidification direction. i.e. Ni Al has anisotropic properties. Therefore. each of the samples for the tensile tests was produced from a unidirectionally solidified rod so as to have a given direction of solidification.

To produce the test samples. a unidirectional solidification device illustrated in FIG. 3 was utilized. The device of FIG. 3 has a quartz tube 2 which has a lower end sealed with a heat resisting material I for retaining a sample. The quartz tube is supported and can be moved up and down by a support 8. There is provided a heat resisting glass tube outside of the quartz tube 2 for the purpose of covering the inner and outer circumference of the tube 2 with an inert gas. An air tight sealing member 7 is provided on the upper end of the glass tube 5 and has a small tube 6 for introducing an inert gas into the quartz tube 2 and the glass tube 5. A high frequency induction work coil 4 surrounds the glass tube 5. Since the upper and circumferential parts of the quartz tube are covered by the sealing member 7 and the heat resisting glass 5, the inert gas introduced through the small tube 6 fills the inside of the quartz tube. and covers the outer peripheral portion of the quartz tube 2 to shut out the atmosphere. The inert is discharged to the atmosphere through the lower end of the glass tube 5.

To obtain a unidirectional solidified rod by using the above-described device. a sample I was placed in a bed 3 of alumina powder (Al O;,) which bed is contained in the quartz tube 2. Then the air inside of the quartz tube 2 was replaced with argon gas by continuously supply ing the argon gas through the small tube 6. After the argon gas has purged the air from the quartz tube. a high frequency induction current was applied to a high frequency work coil 4 to melt the sample I by means of heating it from the lower end or part thereof. The support 8 was gradually moved downward so that the sample 1 was solidified from the lower end thereof. In this manner a unidirectionally solidified rod for making test pieces or samples with the direction of their crys* tals arranged in the longitudinal direction was pro duced.

For the tensile tests. the test piece was made from the above stated unidirectionally solidified rod by machining the rod to a size with a length of 35 mm. a diameter in the parallel portion of4 mm and a length in the parallcl portion of 17 mm. The test piece was maintained in the test temperature ranging from l.0O0-l.lt)t)C for minutes and then tested at a tensile speed of 2.5 mm/minutes. The test results are represented in terms of tensile strength (kg/mm For the oxidation test which examined the oxidation resisting properties of the sample. a test piece was prepared by cutting the above stated rod into a test piece hzning a diameter of It) mm and a length of It) mm. The faces of each of the test pieces was polished into a metallic surface. After weighing each of the test pieces. it as heated to I.2(]()C and maintained in an air atmosphere for 21 hours. After completing the period of heating. the weight of each test sample was again measured and the amount ol o\idation would be indicated by any increase in the weight of the sample. From this test the oxidation weight (AWg) and the spalling (flaking. exfoliation) weight (AWf) were obtained in the following manner. Assuming that the weight of the test piece before the oxidation test is W0. and that its surface area is So. that the weight of the test piece after the oxidation test is Wg and that the weight of the oxides. which spalled or flaked off. is Wf. the oxidation weight (AWg) can be expressed as follows:

Il'g lijr- H'n A li The spalling weight (AWf) then can be expressed as follows:

These weights are expressed in mg/cm Smaller values for the oxidation weight (AWg) or the spalling weight (AWf) indicate a better oxidation resisting property of the alloy.

For testing the toughness. test samples were pressed with a Vickers hardness tester which is generally employed in measuring the toughness of superhard alloys. The toughness thereof was judged by the load which caused cracks around the trace of pressure or the indentation which was formed by the load during the tests. Samples that tend to produce such cracks under lighter loads were judged to be too brittle.

The samples were subjected to varied Vickcrs loads of l. 5. It). 20. 3t) and kg. respectively. with each of the loads being impressed into three different areas of each sample. and each of the indentations was inspected or examined to determine whether or not cracks were produced by a given load. The maximum load (kg) that produced no cracks in all of the three im pressed indentations is considered to be the degree of toughness.

Test Example I FIG. 4 illustrates the relation between the tensile strength at l.()(l0C for nickel-aluminum-molybdcnum alloy as the percentage of molybdenum is changed from 0 to approximately 14%. The curves H. I and .l of FIG. 4 correspond to lines h. i andj in the diagram of FIG. 1. respectively. and the curves H. I and J, respec tivcly. represent the tensile strength at I.OUOC of the nickcl-aluminum-molybdenum alloy having the composition represented by the lines I1. i andj of FIG. 1. The percentage of the nickeI-aluminum-molybdcnum alloys at any desired point on the curves. H. I and J are obtained from the lines Ii. i and j of FIG. I by referring to the contents of molybdenum of the said given point. respectively. Thus. the line 11. represents the composition of alloy wherein the aluminum of the Ni Al is replaccd with molybdenum and is a line connecting Ni; Al with the Ni;.Mo (FIG. 1 The linej represents the composition of an alloy wherein the nickel of the Ni Al is replaced with molybdenum while the line i' is position between the lines I: and wherein molybdenum is added to the Ni Al.

The tensile strength curves H. I and .l of FIG. 4 illustrate the maximum tensile strengths 56 kg/mnr". 44

kgrlnin and Mt lsgrmin [e-qccti cl t. and the ltltt\l' mum strengths and obtained when the atomic percent of molybdenum is between llllr'. lhe LftIHBs also il lustrate that a high tensile strength is obtained over a range of (will niohbdenuni in the nielsclalltiminunr moly denum 'lllo Thwsc carves reveal that the clet'llILtl temperature ten ile strength is more than [.5 times as much as the tensile strength of l) kgrmm at l ""i .\l tor l twat csisting alloy. Tht addi tit ol mt vbtlenuni in excess of ill! causes an abrupt decrease oi the high temperature tensile strength lor the alloys. This t'lccicasc is l clicvctl to result from the fact that uhcn molybdenum is in L\c'=c\\ oi llci. the contents of the W'i; l\lt in the allo c .cccds the content of the Ni Al in tlic allo On the other hand when the content ot tltiitlticttttlil is le s than ML the degree ol strengthening the solid solution of :li tl due to molyh dcnum is considcrablv Ion.

lest Example ll Fl('1. 5 illustrates a relationship between the toughness at room temperature for the nickel aluminumniolvbdcnum alloy and a var ing percentage content of molybdenum. The illustrated allo 's include a range of the basic constituent oi the nickel based alloy of the present in\ention. The test samples \vcrc selected from a nieltel aluminum-inol bdciunn allov having a compo sition re resented by the line it in Flt) l and the con tents of the nickel and the aluminum in each test sam ple are obtained from the line h of FIG. 1 by referring to the percentage content ot the niolyi' denum of each test sample '1 he toughness ot each of the test samples is illustrated from the data of FIG. 5.

As will be apparent from the curve ot- HO. 5. in the case of more than ttl' tnol). hdenum. the toughness ex ceeds the critical load of i kg for the toughness test and the degree of toughness is too high to measure by this measuring method. Thi reveals that the alioys con ing of the elements nickelatluminum-mol hdenuni which alloys are Wltlitlt the rangc ol the basic constitu' ent of the nickel base alloy oi" the present invention. nameh those allots with more than lll ni molybdenum in content have a high toughness of more than 5t) ltg which is Z 5 times as much as the toughness of 20 kg of the conventional alloy consisting of Ni /\l without molybdenum. Thus the alloys oi the present invention have oierconie the problem oi insufficient toughness which was experienced in the conventional heat. res ing alloys and thus are altoys sith a good ductility Test Example [I] In FIG. fr the results oitensile tests at l.l()t)(' ot an alloy containing a basic constituent of nickel aluminum-molybdenum with the 759i nickel, 15% alu minum and lttii tlttllj lit tjltttllt and an additive constita cnt consisting oi one or more elements of titanium. chromium. /irconinni. nioiuuin. tantalum and tungsten being added to the alloy are illustrated with the per centage ot' the atlditixe constituent being from U 5 atomic percent The ordtnutc represents the tensile strength tkg mnr'l and the abscissa represents the content ot'the additive element or constituent. in H0. (J

the curve R represents the maximum tensile strength for respective contents of the atlditnc element and the curve T represents the nnnimuin tensile strength Fig. 6 shows that the allo s obtained by the addition of the additive element or constituent to the basic constituent of uicltcluluntiniun-molybdenum provides a tensile strength ranging from limucen the curves R and T. As

(til

seen in Hi 1 the minimum addition oi the udditi\c consti uent causes an abrupt increase in the tensile strength to obtain the maximum value in the content ranging from (l.52.5% the maximum tensile strength is 5 kgrirnn and the lower limit of the strength is 4. kgrmm Compared with the tensile strength of 38 kgrmrn of the nickclailuminunr molybdenum allo vvithout containing the additive element. the tensile strength of the nickel-aluminumttiol \l7del|lttt'l allo containing the additive constituent has an increase oi 15 to 4W Additions ol the additive constituent in excess of 3? however causes an abrupt decrease in the tensile strength.

lest lisaniple l\" Results ofoxidation resistance tests are illustrated in hit 7. The alloy to l e tested consisted of a nickeltllltttliillll'll'illtllyl' Lldtltlllt basic constituent consisting of 75' nickel. 15% aluminum and it)"; molybdenum and an additive constituent of H.652 niobium. Added to this cterncnt was hi1; silicon and the altots ere heated at IQIHl C in an air atnusphcrc for 1! hours. The weight increase due to oxidation tmgrcm") is represented on the ordinate and the content of silicon is rep resented on the abscissa. The results of the oxidation tests as shown in FKS. 7. are such that the addition of (|.7'r silicon reduced the weight increase due to oxidation from 23.5 mgleni for the alloy consisting of the basic components plus the niobium as an additive Constitnent without silicon to l.7 mg cnr This means that the addition of silicon imparts the oxidation resisting propcrt to the allot. Particularly the addition of k4? silicon minimi/cs the eight increase due to oxidation to lcss tlian I nig 'em and thus provides an allo with a greatly improved oxidation resistance. However. the addition of silicon in excess of 4% causes an increase in the weight increase due to oxidation and in excess of (it? lowers the cilect of improxing the oxidation resistance. lt was continued that the effect of enhancing the o\idation resistance by addition of silicon as illustrated by HQ. 7 also occurs when silicon is added to the alloys of the present invention which contain an additive agent suh as titanium. chromium. Virconiuni. tantalum and tungsten.

The spalling eight was measured simultaneous with the measurement of the weight increased due to oxida tion and presents four times as much as the weight increase due to oxidation. The addition of silicon also re duces the spalling weight in a manner similar to the decrease of the oxidation weight. This proves that the oxidation in the nickel-aluminum'molybdcnum alloy proceeds with spalling. According to other tests. the addition of silicon to the nickel aluminum alloy which contains no molybdenum did not produce any improve merit in osidation resistance.

Results ot a tensile test at l l i()( of alloys which consist oi nickel-a]uminunrinolvhdcnum allo with a basic constituent containing 755? nickel, T592 aluminum. ltlk molybdenuman additive constituent of am tantalum and various amounts of silicon in a range of 0-41"? are iliustratcd in FIG. 8. The tensile strength tkglmm J is represented by the ordinate and the content otsilicon is represented by the abscissa. As seen in FIG. 8, the tensile strength follows substantialh a linear decrease with an increase in the content otsihcon and the tensile strength oi the nickcLaIuminummoi l dcnum allo \vithout containing silicon is approxand imately 50 kg/mm". The nickel-aluminum molybdenum alloy containing 6% silicon has .a tensile strength lower to approximately 30 ltg/mm'i The decrease in the tensile strength at high temperatures due to the addition. of silicon is commonly found in all of the nicke1a1uminummolybdenum alloys containing one or more of the additive elements and silicon. In view of the decrease of the tensile strengths at high temperatures, the addition of excessive silicon is not desirable. Since the conventional Ni=,Al alloy has a tensilc strength of less than 19 kg/mm at 1.000C and less than kg/mm at 1.100C. it is concluded that the alloys having a tensile strength of 30 lag/mm at 1.100C is excellent particularly if it has a heat resisting strength or property. Embodiment l Twenty-four samples of the alloys according to the present invention were prepared from electrolytic nickel. high purity aluminum, high purity molybdenum and high purity titanium, chromium. zirconium, niobium. tantalum and tungsten were prepared by melting in the argon gas atmosphere. These samples which have an atomic percent composition set forth in Table l were su bjccted to test for tensile strength at 1,100C, for oxidation resistance at 1 200C for 21 hours and tough ness test at room temperature. The results of the tests for each sample are given in the Table 1. The alloy numbers 1 through vl7 have a composition close to the point K within the range of the basic constituents shown in FIG. 1. The alloys 18 through and the alloys 2] through 24 have. respectively. compositions close to the points L and M which are both within the range of the basic constituents shown in F10. 1.

For reference. the following Table 1 gives the results of the same tensile tests, oxidation resistance test for As \till be apparent from Table l. the alloys 01 this invention contain the basic constituent of nickc1 a1uminum-molyhdenum and at least one element of titanium. chromium. zirconium. niobium. tantalum and tungsten present extremely high tensile strengths at e1evated temperatures. For example. the tensile strength of alloys 1 through 17 consisting of the alloy K which has a composition of point K in FIG. I and additive element such as titanium is from 43 to 54 leg/mm" approximately and this is higher by 5 to 16 kg/mm than the elevated temperature strength of 38 kg/mm of the alloy K without any of the additive elements. Alloys of the present invention having a base constituent comprising the alloys L or M and one or more additive elements hereinbefore described have a tensile strength at high temperatures from approximately 35 to 39 1tg/mm and from about 30 to 32 kg/mm respectively. These alloys are higher in tensile strength by 5 to 9 kg/mm' and by 5 to 7 kg/mm in comparison with the tensile strength of 30 kg/mm and the tensile strength of kg/mm of the basic alloys L and M. respectively. None of the alloys presented have a toughness of less than 50 kg. This means that the alloys of the present invention have excellent toughness properties at room tempera ture. In view of the fact that the tensile strength at high temperature for lnconel 713C (the conventionally known excellent heat resisting alloy] is 14.0 kgfmm it can be concluded that the tensile strengths at high temperatures ranging from to 54 kg/mm for the alloys 39 of the present invention are extremely good.

the alloys having a composition equal to those taken at 1 points K M of FIG. 1 and for lnconel 713C. which is a conventionally known heat resisting alloy.

Embodiment 11 Some of the same alloys as those used in the table of Embodiment I. and a high purity silicon were melted under an argon gas atmosphere to prepare six kinds of alloys having a composition shown in Table 1!. Alloys number 30 through are equivalent to the alloys number 1. 3, 5, 7, 10 and 13 which are tabulated in Table 1 and have approximately 2% silicon added TABLE I Tensile test Weight in- Alloy Composition (Atomic percent) at 1 100C crease due Tough- No. Strength Elongato oxidation ness Ni Al Mo Ti Cr Zr Nh Ta W (kg/mm") tion (70 (mglcm (kg) 1 74.16 14.79 9.85 1.20 49.9 8 28.7 more 2 73.26 14.61. 9.73 2.40 53.6 8 33.0 than 3 74.23 14.80 9.86 1.11 43.8 10 4.8 4 73.42 14.63 9.76 2.19 43.8 10 3.5 5 74.58 14.87 9.91 0.64 44.0 6 28.3 6 74.12 14.77 9.85 1.26 42.9 7 36.3 7 74.59 14.87 i 9.91 0.63 48.0 9 23.5 8 74.12 14.78 9.85 1.25 49.1 9 29.0 9 73.16 14.59 9.72 2.53 44.7 7 34.0 10 74.82 14.92 9.94 0.32 49.1 9 5.3 1 l 74.56 14.88 9.91 0.65 50.7 1] 7.8 12 74.06 14.77 9.85 132 52.3 8 10.8 13 74.83 14.92 9.94 0.31 48.7 8 21.9 14 74.58 14.87 9.91 0.64 52.7 11 26.1 15 74.31 14.83 9.88 0.65 0.33 53.6 10 49.5 16 73.50 14.70 9.80 1.00 1.00 53.0 7 5.0 17 73.35 14.67 9.78 1.00 1.20 51.2 6 48.4 18 69.16 19.76 9.88 1.20 38.1 11 15.4 19 69.07 19.74 9.87 1.32 39.0 9 8.7 20 69.30 19.80 9.90 100 35.0 12 13.4 21 66.79 22.93 9.97 0.31 36.0 26 3.0 22 66.56 22.85 9.94 0.65 30.4 14 5.4 23 66.00 22.65 9.85 1.50 32.2 20 4.7

t 24 66.56 22.85 9.94 0.65 32.1 19 2 6 K 75 15 10 v- 38.0 2 39.3 1. 20 10 30.0 12 7.0 M 67 23 10 25.1 21 211 lnconel 74.2 6.1 4.2 H: 0.012 11:0.8 Cr: 1.. 5 14.0 2.5 713C Zr 0.1 Nb: 2.0 C: 0 l

thereto. These alloys numbers 30 through 35 were each tested for tensile strength of 1.100%. oxidation resis tance at 1.2U(]C for 21 hours and toughness property at room temperature by the same methods that were utilized for the alloys of Embodiment l. The results of these tests are given in the following Table ll.

dustry or device which require operation at ele\ated temperatures.

Although minor modifications might be suggested by those versed in the art. it should be understood that we wish to employ within the scope of the patent granted hereon all such modifications as reasonably and prop- TABLE ll Tensile test Weight in- Tough- Allo Composition (Atomic percent) at 1 100C crease due ness No. Strength Elongato oxidation (kg) Ni Al Mo Ti Cr Zr Nb Ta W Si (kglmm lion ['7rj (mg/cm") 72.67 14.48 9.66 1.18 2.111 39.3 3.9 2.4 more 31 72.74 14.50 9.67 f l ()8 2.0] 36.2 7.0 1.7 than 50 32 73.05 14.56 9.71 (1.62 2.06 37.1 4.0 5.2 33 73.06 14.56 9.71 0.61 2.06 43.9 5.0 1.7 34 73.32 l4.6(l 9.74 0.31 2.03 44.3 3.8 1.2 35 73.33 14.71 9.74 0.31 2.03 45.4 7.0 1.7

When a comparison of the alloys 30 through 35 of go the present embodiment is made with the alloys numhers I. 3. 5. 7 10 and 13 which do not contain silicon as shown in the tabulation of Table l. the alloys of this embodiment exhibit from one-third to one-fifth of the amount of weight increase due to oxidation as their 2 corresponding alloys which contained no silicon. This means that the oxidation resistance of these alloys of this embodiment was greatly improved by the addition of silicon. The tensile strengths of the alloys of this embodiment however. are somewhat lower by approximately 10-20% due to the addition of silicon. ln view of the fact that the tensile strength of the alloys of this embodiment at l.1(lUC range from 36 to kg/mm and the weight increase due to oxidation after heating at 1 .2()UC for 21 hours is from 1.2-5.2 mg/cm it is believed that the alloys of this embodiment are excellent in high temperature strength and in oxidation resistanee. It is apparent from a comparison of test results of Table 11 with the test results for lnconel 713C in Table I in which the lnconel 713C has a tensile strength of 14.2 kg/mm at l.l()0C and a weight increase due to oxidation of 2.5 mg/cm when heated to 1.0U0C for 21 hours. In addition the test results of the alloy numbers 30 through 35 show that at room temperature, the results of the toughness rest was more than kg. This clearly teaches that these alloys have excellent toughness particularly at room temperature.

In summary, the heat resisting alloys of the present invention which consists of three basic elements such as nickel. aluminum and molybdenum as a basic con stituent whose composition falls in a range defined by the points. A, B, C and D in FIG. 1 and includes 0. l3 atomic percent of one or more elements of titanium. chromium, zirconium, niobium, tantalum and tungsten exhibit greatly improved tensile strengths at elevated temperatures and excellent toughness at room temperature. The alloys consisting of the basic constituents comprising nickel-aluminum-molybdcnum having the above-mentioned composition. one or more additive elements mentioned above and from 0.5-6 atomic percent silicon exhibit high tensile strengths at elevated temperatures. excellent toughness properties at room temperature and also having excellent oxidation resis tance properties at elevated temperatures. Thus. the alloys of the present invention are versatile as heat rcsisting materials which are applicable for use in steam turbines. gas turbines, devices for use in chemical in erly come within the scope of our contribution to the art.

We claim:

1. A heat resisting alloy which has excellent mechanical strength. toughness and oxidation resistance at elc vatcd temperatures in the range of l.OO()-1.2()()C. said alloy consisting essentially of 93-98.) atomic percent of a basic constituent comprising nickel. aluminum and molybdenum in the following atomic percents of the basic constituent. nickel 62-83%. aluminum l 1-2671. and molybdenum 6.42%; 0.14% atomic percent of a second constituent consisting of at least one element selected from a grou pconsisting of titanium. chromium. zirconium. niobium. tantalum and tungsten; and 1-4 atomic percent silicon.

2. A heat resisting alloy according to claim 1. wherein the silicon is present in a range of 2-4 atomic percent.

3. A heat resisting alloy according to claim I, wherein the second constituent is present in a range of 0.52.5 atomic percent.

4. A heat resistance alloy which has excellent me chanical strength. toughness and oxidation resistance at elevated temperatures in a range of 1.00()1.2UUC. said 'alloyconsisting essentially of the following atomic percentages of constituents:

10.01 25.8447r aluminum;

5.4 6' 11.92892 molybdenum;

l 4% silicon; and

0.1 3% of an additive constituent. selected from a group of elements consisting of titanium. chromium. zirconium. niobium. tantalum. and tungsten. said additive constituents comprising at least one of said elements from said group.

5. A heat resisting alloy according to claim 4, wherein the additive constituent is titanium in the range of 1-2.4 atomic percent.

6. A heat resisting alloy according to claim 4 wherein the additive constituent is chromium in a range of 1.0-2.5 atomic percent.

7. A heat resisting alloy according to claim 4. wherein the additive constituent comprises zirconium in a range of ().5l.5 atomic percent.

8. A heat resisting alloy according to claim 4. wherein the additive constituent comprises niobium in a range of U.52.6 atomic percent.

(it I l3 A heat resisting iillo according to claim 4, wheiein the additive constituent comprises both titanium and yirconium 14. A heat resisting nllo according to claim 4. wherein the silicon is in a range of 10-21%; the nickel is in a range of 7167-7333711 the aluminum is in a range of l4.48-l4.7l1i; the molybdenum is in a range of )hn JJM/; and the additive constituent is in a range of (L3 1- l A l 8%.

15. A heat resisting alloy according to claim 4, wherein the silicon is in a range of 2-471. 

1. A HEAT RESISTING ALLOY WHICH HAS EXCELLENT MECHANICAL STRENGTH, TOUGHNESS AND OXIDATION RESISTANCE AT ELECTED TEMPREATURES IN THE RANGE OF 1,000* -1,200*C, SAID ALLOY CONSISTING ESSENTIALLY OF 93-98.9 ATOMIC PERCENT OF A BASIC CONSTITUENT COMPRISING NICKEL, ALUMINUM AND MOLYBDENUM IN THE FOLLOWING ATOMIC PERCENTS OF THE BASIC CONSTITUENT, MICKEL 62-83%, ALUMINUM 11-26%, AND MOLYBDENUM 6-12% 0.1-3 ATOMIC PERCENT OF A SECOND CONSITITUENT CONSISTING OF AT LEAST ONE ELEMENT SELECTED FROM A GROUP CONSISTING OF TITANIUM, CHROMINUM, ZIRCONIUM, NIOBIUM, TANTALUM AND TUNGSTEN, AND 1-4 ATOMIC PERCENT SILICON.
 2. A heat resisting alloy according to claim 1, wherein the silicon is present in a range of 2-4 atomic percent.
 3. A heat resisting alloy according to claim 1, wherein the second constituent is present in a range of 0.5-2.5 atomic percent.
 4. A heat resistance alloy which has excellent mechanical strength, toughness and oxidation resistance at elevated temperatures in a range of 1,000*-1,200*C, said alloy consisting essentially of the following atomic percentages of constituents: 56.42 - 82.502% nickel; 10.01 - 25.844% aluminum; 5.46 - 11.928% molybdenum; 1 - 4% silicon; and 0.1 - 3% of an additive constituent, selected from a group of elements consisting of titanium, chromium, zirconium, niobium, tantalum, and tungsten, said additive constituents comprising at least one of said elements from said group.
 5. A heat resisting alloy according to claim 4, wherein the additive constituent is titanium in the range of 1-2.4 atomic percent.
 6. A heat resisting alloy according to claim 4 wherein the additive constituent is chromium in a range of 1.0-2.5 atomic percent.
 7. A heat resisting alloy according to claim 4, wherein the additive constituent comprises zirconium in a range of 0.5-1.5 atomic percent.
 8. A heat resisting alloy according to claim 4, wherein the additive constituent comprises niobium in a range of 0.5-2.6 atomic percent.
 9. A heat resisting alloy according to claim 4, wherein the additive constituent comprises tantalum in a range of 0.32-1.32 atomic percent.
 10. A heat resisting alloy according to claim 4, wherein the additive constituent comprises tungsten in a range of 0.31-0.64 atomic percent.
 11. A heat resisting alloy according to claim 4, wherin the additive constitueNt comprises both niobium and tungsten.
 12. A heat resisting alloy according to claim 4, wherein the additive constituent comprises both chromium and tantalum.
 13. A heat resisting alloy according to claim 4, wherein the additive constituent comprises both titanium and zirconium.
 14. A heat resisting alloy according to claim 4, wherein the silicon is in a range of 2.0-2.1%; the nickel is in a range of 72.67-73.33%; the aluminum is in a range of 14.48-14.71%; the molybdenum is in a range of 9.66-9.74%; and the additive constituent is in a range of 0.31-1.18%.
 15. A heat resisting alloy according to claim 4, wherein the silicon is in a range of 2-4%. 